Field of the Invention
The present invention relates to degradation detection for a running wheel of a running vehicle.
Description of the Related Art
The applicant has been developing and manufacturing overhead travelling vehicles that travel in overhead spaces of clean-rooms or the like. The structure of the running vehicle part in the overhead travelling vehicles is disclosed in Patent Literature 1 (JP2002-308404A), for example. In the overhead travelling vehicles, a pair of front and rear vehicle units are each provided with following wheels and guide rollers, and a driving wheel unit is further provided so as to span the pair of front and rear vehicle units. The driving wheel unit is provided with a running motor and a running wheel (driving wheel), and the running wheel is biased so as to be kept in contact with the travel rail at a predetermined contact pressure. The running wheel is solid and made of polyurethane rubber, for example.
As a consequence of repeated running, the running wheel made of synthetic resin develops a rough surface due to abrasion. The rough surface may lead to the running wheel bursting, in which case the surface of the running wheel separates, and then it becomes necessary to stop the overhead travelling vehicle and replace the running wheel. The degradation is not uniform between the running wheels. Therefore, it is necessary to choose whether to replace the running wheel well before the degradation becomes problematic, or to let a burst or the like of the running wheel occur due to delayed replacement and thus to take the risk of the running route being impassable due to the stopped overhead travelling vehicle.
Patent Literature 2 (JP3509330B) discloses detecting the decrease in the pressure of the tires of a four-wheel automobile based on the decrease in the diameters of the tires. Patent Literature 2 detects a driving wheel slip ratio according to the ratio of the number of rotations of the driving wheel and that of the following wheel. It concludes that, in the plot of the torque applied to the driving wheel and the slip ratio, the slip ratio at 0 torque reflects the decrease in the diameter of the driving wheel due to the decrease in the tire pressure. However, this method does not work for degradation of the surface of the running wheels caused by abrasion or the like. The inventor has confirmed this fact by experiments.